The invention relates to a pressure sensor component with a pressure connection element, in particular with a hose connection element, which can be mounted on the component-mounting top side of a printed circuit board. Such components are preferably surface-mounted (so-called SMD; SMD=surface mounted design) for space-saving reasons. The pressure measurement is usually carried out in accordance with the piezoresistive principle. Alternatively, it is possible to work with capacitive measurement principles. A semiconductor chip generally composed of silicon is used, as a rule, as the pressure sensor. In the case of piezoresistive measurement, the chip surface has arranged on it a thin silicon diaphragm electrically coupled to pressure-dependent resistors which are likewise formed in the silicon substrate and are connected in a bridge circuit. The semiconductor chip likewise comprises a circuit, assigned to the sensor, for amplification and correction of the signals and for trimming and for compensation of the sensor.
In order to measure the pressure, it is necessary to establish contact between the medium to be measured and the pressure sensor, that is to say the medium to be measured must be brought up to the sensor or the prevailing pressure must be transmitted to the sensor. Therefore, the pressure sensor is disposed in a housing which is open on one side. The pressure-sensitive surface of the sensor can thus make contact directly or indirectly with the medium to be measured. In order to prevent damage to the pressure sensor by the medium, it is customary to cover the surface of the semiconductor chip with a flowable filler, generally a plastic gel. The filler is chosen such that it passes on the pressure uncorrupted to the sensor.
If the medium to be measured is the medium which surrounds the pressure sensor component, the open pressure sensor component as such can be used. If the medium to be measured is not the same as the surrounding medium, the medium to be measured must be brought up to the sensor separately from the surrounding medium. For this purpose, use is usually made of a hose or tube system connected to the sensor component.
It has heretofore been customary in such cases to use pressure sensors embedded in a special housing with a hose connection. As a rule, these housings are considerably larger than the corresponding housings for the same sensor without a hose connection. This is disadvantageous both from cost standpoints and with regard to the subsequent application of the components. Moreover, the pressure sensor components with a hose connection obtainable heretofore have a defined connection diameter, which is fixed from the outset, with the result that the user of the pressure sensor is not left with any choice options in respect of the hose connection that is used.
A further disadvantage of the prior art pressure sensor components with a hose connection resides in the production of the components. The hose connection is fitted only after the open pressure sensor has been fully completed and the semiconductor chip has been covered with the filler. The hose connection is then bonded onto the pressure sensor component. In other words, an additional step, namely the permanent bonding of the hose connection, is necessary for the production process. In addition, it is necessary to test the adhesive bond in terms of its tightness. These additional steps are time and cost-intensive.
German published patent application DE 43 17 312 describes a pressure sensor with a pressure chamber arranged in a plastic housing. The pressure chamber has a tube connector which engages in a connection tube of a housing cover. It is described that at low pressures it may suffice to effect sealing between tube connector and connection tube with potting compound which is used to cover ceramic chip capacitors.
It is accordingly an object of the invention to provide a pressure sensor component with a hose connection, which overcomes the above-mentioned disadvantages of the heretoforeknown devices and methods of this general type and which can be produced simply and cost-effectively. At the same time, the size of the housing should be kept as small as possible and, expediently, it should be possible to use the same base housing form as for a corresponding open sensor component without a hose connection. In addition, the pressure sensor component should be suitable for the connection of hoses of different diameter.
With the foregoing and other objects in view there is provided, in accordance with the invention, a pressure sensor component for mounting on a component-mounting surface of a printed circuit board, the component comprising:
a base body formed with a chip carrier and a semiconductor chip mounted on the chip carrier;
a flowable filler completely covering the base body;
a plurality of electrical connections to be routed out from the base body;
a tubular pressure connection element having an end fastened on the base body, the flowable filler filling interspaces formed between the end of the pressure connection element and the base body at least partially and sealing the pressure connection element gastightly against the base body.
In accordance with an added feature of the invention, the pressure connection element is fastened on the base body by an attachment selected from the group consisting of adhesive bonding, welding, and clamping.
In other words, the pressure sensor component according to the invention comprises a base body, which, in principle, may correspond to a customarily used open pressure sensor component, that is to say to a component without a hose attachment, and a pressure connection element matching the base body.
The distinctive feature of the invention is the fact that the base body and the pressure connection element are sealed with respect to one another with the flowable filler which is likewise used to fill the chip carrier and to cover the semiconductor chip. The base body is preferably configured to be open on one side and encompasses the semiconductor chip mounted on the chip carrier and connections which are contact-connected to said chip. The pressure connection element is advantageously placed onto the base body and encloses the opening in the base body in which the semiconductor chip is situated. This has the advantage that the filling of the chip carrier and hence the covering of the semiconductor chip and the sealing between base body and pressure connection element can be carried out together.
The flowable filler used is one which is sufficiently elastic to transmit pressures to the pressure sensor without corrupting the measurement results. With respect to the media usually to be measured, the filler should be largely chemically inert and be simple to handle. The filler is preferably a plastic gel, in particular a silicone-based gel.
As already mentioned, the base body of the pressure sensor component can, in principle, have any form and configuration which is usually used in the case of pressure sensor components which can be mounted on printed circuit boards. The base body expediently comprises a chip carrier made of plastic, in particular made of thermoplastic, which has an essentially planar chip carrier area on which the semiconductor chip with an integrated pressure sensor is arranged. Embedded in the plastic composition are a plurality of connections which project laterally from the chip carrier. The semiconductor chip and connections are contact-connected to one another in a customary manner for example by bonding wires. Alternatively, the chip can be arranged on a metallic lead frame having integrated connections. The chip carrier preferably has, at its edges, a side wall which has a height projecting above the chip surface and encloses the chip carrier. This side wall bounds the opening in the base body through which the medium to be measured is fed to the pressure sensor for the pressure measurement. The side wall of the base body expediently terminates in planar fashion at its upper end. The pressure connection element is placed onto this side wall.
The pressure connection element according to the invention is configured in such a way that its end region which bears on the side wall of the base body is forked. In other words, that end of the outer wall of the pressure connection element which faces the base body engages about the upper end region of the side wall. One end or partial region of that end of the outer wall of the pressure connection element which faces the base body in this case runs along the outer side of the side wall of the base body; another end or partial region of that end of the outer wall of the pressure connection element which faces the base body runs along the inner side of the side wall of the base body.
In order to achieve good sealing between the base body and the pressure connection element, the interspace situated between that end of the pressure connection element which faces the base body and the end region of the side wall of the base body, which end region faces the pressure connection element, is filled preferably as far as possible completely with the flowable filler, thereby forming gastight sealing between base body and pressure connection element.
In a particularly expedient manner, the interspace is filled at the same time as the semiconductor chip is covered. For this purpose, after the pressure connection element has been emplaced and fastened on the base body, the flowable filler is introduced through the opening in the pressure connection element into the base body cavity. The filling height and the length of the inner end regions of the pressure connection element are in this case coordinated with one another in such a way that the filler is drawn by capillary forces into the interspace between pressure connection element and side parts of the base body. Therefore, only one filling operation is necessary in order to provide the inner space of the base body with filler and to seal the base body and pressure connection element with respect to one another. The pressure sensor components according to the invention can therefore be produced extraordinarily simply and cost-effectively.
In accordance with an additional feature of the invention, the base body has a side wall encompassing the chip carrier and the semiconductor chip and forming an end region projecting towards the pressure connection element, the end of the pressure connection element engaging on both sides about the end region of the side wall, and wherein the base body and the pressure connection element are sealed against one another with the flowable filler.
In accordance with another feature of the invention, the side wall is formed with a flow stop edge for the filler, and the end of the pressure connection element facing the base body has an inner wall extending along an inside of the side wall of the base body for covering the flow stop edge peripherally inside the inner wall.
In order to produce open pressure sensor components, chip carriers with a peripheral flow stop edge along the inner side of the side wall of the base body are preferably used. The effect of this flow stop edge is that during the filling-in process, the filler does not penetrate beyond this edge into regions of the base body which ought not to be contaminated by the filler. Base bodies of this type can also be used within the scope of the invention. In order to ensure that the interspace between the end region of the side wall of the base body and the end of the emplaced pressure connection element is sufficiently filled, that end region of the pressure connection element which runs along the inner wall of the base body side parts is designed with a length such that it projects above the flow stop edge and covers the latter. In this way, capillary forces which draw the filler into the interspace between pressure connection element and base body side wall can also become effective in the region of the flow stop edge. With appropriate matching of the pressure connection element, then, it is also possible to use the customary open pressure sensor components with flow stop edge unchanged for the inventive pressure sensor components with connection.
In accordance with a further feature of the invention, the pressure connection element is formed with at least one fastening lug adapted to engage in an associated fastening cutout or opening formed in the base body.
In accordance with an alternative feature of the invention, the base body has at least one fastening lug formed thereon adapted to engage in an associated fastening recess formed in the pressure connection element.
The pressure connection element can be fastened to the base body particularly securely if two or more fastening lugs are formed in the pressure connection element, which lugs can latch into corresponding fastening openings or fastening cutouts in the base body. If only two fastening lugs are used, they are preferably situated on opposite sides of the pressure connection element. The fastening lugs are preferably formed in the region of the outer ends of the pressure connection element which run along the outer side wall of the base body in the assembled state. The fastening lugs particularly preferably project in the direction of the base body at the end-side end region of the outer ends of the pressure connection element. Alternatively, it is likewise possible, of course, to fit the fastening lugs in the base body and the associated fastening openings or cutouts in the pressure connection element.
In order to facilitate the engagement of the fastening lugs in the associated fastening openings or cutouts, the fastening lugs may be beveled or rounded in their edge region.
In accordance with again an added feature of the invention, the pressure connection element is formed with a conical connector for attachment of hoses of respectively different diameters.
The pressure connection element according to the invention is preferably adapted for the connection of a hose through which the medium to be measured can be fed to the pressure sensor in the base body. In order to enable the use of different hose diameters, it is possible either to use sets of pressure connection elements which differ only in respect of the hose diameter to be used. Preferably, however, a pressure connection element is used which is suitable for fitting hoses having different diameters. A pressure connection element having a conically inleading connector may be mentioned by way of example, onto which connector hoses having different diameters can be pulled. The suitable hose diameter can then be chosen in accordance with the respective application.
In accordance with a concomitant feature of the invention, the flowable filler is a gel, such as a silicone resin-based gel.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a pressure sensor component with hose connection, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.